Present construction machines, such as wheel loaders, typically include a slab lift arm which is mounted to a frame of the machine by various connection means. Box boom lift arms may be used in place of the slab lift arms on some wheel loaders to gain higher strength capabilities. Some of these box boom lift arms have a hollow unitary structure made from two or more castings connected by a transversely welded midsection. The box boom lift arm is generally connected to various components, such as a frame or tilt linkage assembly, with configurations that increase strength capabilities, visibility and effectiveness of the machine.
During operation of the wheel loader; the box boom lift arm and tilt linkage assembly are subjected to a high degree of loading, some of which may be severe. Therefore, it is critical that each component has sufficient configuration and connection to one another to provide the strength necessary to withstand these loads and forces while limiting the weight so as to not affect overall machine performance. The strength requirements for each of the components of the box boom loader mechanism are coupled with the need to increase visibility for an operator of the machine during operation.
One such design is disclosed in U.S. Pat. No. 4,768,917 issued to Anthony L. Garman on Sep. 6, 1988. In this design, the boom arm is made from two hollow end castings welded together by a welded midsection. The connection of the boom arm to the frame utilizes a pivotal pin joint mounted across the outer walls of the frame. The mounting of the boom arm in such a manner requires that the majority of loading takes place at the pin joint and at the transverse welded midsection of the boom arm which may increase the risk of failure of the welded castings. The tilting arrangement in Garman utilizes a tilt lever that is an elongate member having three distinct areas of connection that withstand the majority of the loads and forces on the machine during operation of the linkage The mass of the tilt lever must be increased in order to withstand the loads and forces incurred which may limit overall performance of the machine. Additionally, visibility of the machine is hampered by the connection of the tilt cylinder at the distal end of the tilt lever.
The present invention is directed to overcoming the problems as set forth above.